Materials and techniques for recovery of metals from wastewater containing metals (e.g., gold) discharged from industries related to mining, plating, surface treatment, inorganic chemistry, and the like have been reported to date.
For example, patent literature 1 discloses a gold adsorbent that is a lignin derivative prepared by adding a phenolic compound to wood powder generated by lumber sawing or the like, further adding concentrated sulfuric acid to perform a reaction, thereby allowing lignin to bind to the phenolic compound, and then isolating a resulting lignin derivative. The prior art technique using such a lignin derivative is problematic in terms of environmental load level from the view points that carbon-fixed woody biomass resources are consumed and utilized and that a chemical such as sulfuric acid is newly added. As other gold recovery techniques that involve performing biological treatment utilizing fungi and plant organic biomass, treatments utilizing organic aminocarboxylic acid-degrading microorganisms (patent literature 2), cyanogen forming and degrading microorganisms (patent literature 3), and cellulose-containing organic resources (patent literature 4) have been reported.
As another example of a method for recovery of various metals utilizing a phytomining technique, non patent literature 1 reports a technique that involves planting Brassica juncea in soil to which gold has been added, and causing the root system to absorb gold, thus resulting in accumulation of about 5-50 nm gold nanoparticles at a concentration of 760-1120 ppm per plant body dry weight. However, this technique has not yet been demonstrated at the practical level since the accumulated gold concentration level as an ability to recover gold is low and soil is the subject for the technique.
Also, patent literature 5 by the present inventors discloses a method for removal of lead utilizing a protonema of a moss plant as an adsorbent. The literature further discloses that lead can be selectively removed from an ash eluate and an artificially mixed solution by the technique using protonema cells of a moss plant as a lead adsorbent, and that the lead-accumulating ability is not significantly inhibited by B, Na, Mg, Al, P, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, and Hg contained in the ash eluate or Cu in the artificial mixed solution. However, the literature does not disclose the presence or the absence of the ability to recover industrially valuable metals, such as rare metals, rare earths, and noble metals, nor the scale of such ability.